Experiments have been performed to study the co-rotating wing-tip vortex pair
produced by a pair of rectangular wings in a split-wing configuration. Detailed
measurements made in cross-sections upstream and downstream of merger reveal,
for the first time, the complex turbulence structure of this flow. The vortices spiral
around each other and merge some 20 chordlengths downstream of the wings. As
merger is approached the vortices lose their axisymmetry – their cores develop lopsided
tangential velocity fields and the mean vorticity field is convected into filaments. The
cores also become part of a single turbulence structure dominated by a braid of high
turbulence levels that links them together. The braid, which quite closely resembles
the structure formed between adjacent spanwise eddies of transitional mixing layers,
grows in intensity with downstream distance and extends into the vortex cores. Unlike
a single tip vortex, the unmerged cores appear turbulent.The merging of the vortices wraps the cores and the flow structure that surrounds
them into a large turbulent region with an intricate double spiral structure. This
structure then relaxes to a closely axisymmetric state. The merged core appears
stable and develops a structure similar to the laminar core of a vortex shed from
a single wing. However, the turbulent region formed around the vortex core during
the merger process is much larger and more axisymmetric than that found around a
single wing-tip vortex.
Flat Plate Wing Standing on a Wall Covered with a Thick Boundary Layer. Wing Characteristics under the Effects of Side Wall Boundary Layer and Wing Tip Vortex.